Since the method for synthesizing a carbon cluster (hereinafter also referred to as “fullerene”), in which carbon atoms are arranged to form a spherical shape or a rugby ball shape, was established, fullerene has been energetically studied. As a result, many fullerene derivatives have been synthesized.
In general, fullerene derivatives have a widely-extended π electron system. Further, characteristically, fullerene derivatives have a relatively small HOMO-LUMO gap (about 1.5-2.0 eV), and also have optical absorption property in a wide wavelength range and highly-efficient light-emitting property via Singlet-to-Triplet intersystem crossing. Further, fullerenes are constituted only by carbon atoms, and at the same time, exhibit multistep reversible redox reaction (6-electron reduction). Attributed to these properties, there are wide range of possibilities for application of fullerene derivatives. For example, it is thought that fullerene derivatives can be utilized for FET, organic EL, solar cells, catalysts, etc.
Regarding a photoelectric conversion device utilizing optical absorption property of fullerene metal complexes, studies of the development of artificial photosynthesis utilizing high electron acceptor ability of fullerenes have been reported. Specifically, there are the following reports: a wet solar cell comprising a monomolecular film prepared by molecules, which are joined via chemical bond using ferrocene (electron donor)-porphyrin (optical absorption center)-fullerene (electron acceptor) on a gold electrode [Eur. J. Org. Chem. 2445. (1999) (non-patent document 1)]; and a wet solar cell, wherein molecules in which fullerene metal complex and porphyrin are joined together are immobilized on an ITO electrode [J. Am. Chem. Soc. 127, 2380, (2005) (non-patent document 2)].
However, these solar cells have the following problems: it is complicated to synthesize a fullerene derivative to be used in a photoelectric conversion device of a solar cell; and desired properties cannot be sufficiently exerted.
Under the above-described circumstances, for example, fullerene derivatives having very high quantum yield of photocurrent generation are desired. Moreover, fullerene derivatives, which have very high quantum yield of photocurrent generation, and which can be easily synthesized, are desired. In addition, solar cells having high power generation efficiency are desired.